If you get 100 Gold Cards you open up a sixth world, Rainbow Palace.
If you get 120 Gold Cards and Kill Sirius at Rainbow Palace, you get
4 new custom parts, 4 new battle arenas and Full Power.
On the screen where you can pick the game mode (adventure, battle, etc.),
repeatedly press the start button until you hear a chime. Then go into battle mode,
where you will find four secret battle courses have been added.